1. Field of the Invention
The present invention relates to a liquid crystal composition, a color filter produced using the liquid crystal composition, and a display device including the color filter.
2. Description of the Related Art
Applications of color filters are increasingly extending such as to include mobile information terminals, personal computers, word processors, amusement machines, televisions, and the like, as well as display panels used in various electric and electronic apparatuses.
These apparatuses are conventionally provided with liquid crystal display devices. Advantages of a liquid crystal display device are that electric power consumption thereof is small and that it is thin. The liquid crystal display devices are generally divided into two groups: transmission display devices including a backlight light source and frontlight reflection display devices which do not include a light source or use an optical waveguide on the entire surface thereof. For a full-color display, usually a color filter is used. For example, a color filter used in a color liquid crystal display, and the like, generally includes red (R), green (G) and blue (B) pixels, and a black matrix formed therebetween for improving display contrast.
Majority of this type of color filters has conventionally been produced using pigment dispersion or staining. The pigment dispersion involves dispersing pigments in a photoresist, coating the photoresist on a glass substrate, and then exposing a pattern and developing. This method is excellent in patterning edge, resolution, evenness of film, and the like. However, this method has problems such that it requires a photoresist process, and that, since pigments are used, adjustment of colors is not as easy as when dyes are used. In addition, when the photoresist is applied on the substrate using spin coating, there will be a large loss of materials, and unevenness of the coating will be large when the area of the substrate is large. In the staining, a transparent resin pattern provided with photosensitivity is stained later onto a gelatin, or the like. Advantages of this method is that it produces a color filter which has a high light transmittance because of transparency of dyes, and that adjustment of colors are easy because there are wide variety of types of dyes. However, the method also has drawbacks such that the number of required steps such as a photoresist step is larger than that for the pigment dispersion.
Other known methods for producing a color filter include printing, electrodeposition, ink jet, and the like. The printing has drawbacks such that, since it prints patterns of respective colors one by one, registration of the patterns is difficult, and that, because of low pixel resolution and uneven film thickness of the resulting color filter, it is difficult to use the color filter produced by the printing method to form a highly detailed image pattern. While, an advantage of the printing method is that it uses materials efficiently. The electrodeposition can provide a color filter which has a relatively high resolution and low unevenness in colored layers, however, it has difficulties such that production steps thereof are complicated and handling of fluids is difficult. The ink jet method has had problems regarding resolution, and that colors of mutually adjacent pixels may be mixed.
The color filters (produced by the methods) described above are light-absorbing color filters, which, in theory, can transmit only one third of the light from the light source, and therefore do not have sufficient brightness. In order to compensate this drawback, for example, in the case of a transmission display device, it can be considered to increase brightness of the backlight. However, this will lead to an increase in power consumption, and will impair the advantage of the liquid crystal display device.
In order to solve these problems, U.S. Pat. No. 00/5,668,614 and WO 00/34,808 have proposed color filters employing a cholesteric polarizer, which do not require a liquid development step. The cholesteric polarizer selectively reflects circularly polarized light having predetermined wavelengths and transmits circularly polarized light having the other wavelengths. Therefore, different from the above-described color filters made of colored resins, the color filter comprising the cholesteric polarizer can reuse the once transmitted light to improve light efficiency, thereby forming a substantially bright color filter. Therefore, this type of color filter is suitable for use in a reflection liquid crystal display. Further, since the production of the color filter comprising the cholesteric polarizer does not require a developing step, and patterns having different selective reflection wavelengths can be formed in a single layer, it is also preferable in view of production costs.
As a method for forming this type of color filter which utilizes the selective reflection by the cholesteric liquid crystal layer, the applicant of this patent application has made a patent application on a method for forming a color filter layer, wherein ink comprising a polymerizing liquid crystal compound is deposited by ink jet (Japanese Patent Application No. 11-343666).
Further, the applicant has made patent application on method for forming color filter, wherein the color filter is formed by irradiating light onto a layer comprising a polymerizing liquid crystal compound and a photo-reactive chiral agent having a certain structure (Japanese Patent Application Laid-Open Nos. 2002-080851 ,2002-080478, and the like). The photo-reactive chiral agent includes chiral sites and sites whose structures change when exposed to light. Since a helical twisting power (HTP) of the liquid crystal is largely altered depending, for example, on an amount of irradiated light, selective reflection over a wide wavelength range including the three primary colors: blue (B), green (G) and red (R) can be accomplished.
When a color filter is produced as described above, first, a solution containing the polymerizing liquid crystal compound and the photo-reactive chiral agent and/or a polymerizing monomer, and the like, dissolved in an organic solvent is coated on a glass substrate. However, it has been found that, if the solution is coated in this state, the resulting color filter will have various minute defects including protrusions, white dots in a colored area, black dots on a white background (black defect), deposition of foreign substances, and the like. The major cause of these defects is existence of very minute foreign substances in the solution. It has been found that, if the foreign substances, although very minute, exist in the solution, they interfere orientation of the liquid crystal layer during production of the color filter over wide areas surrounding the foreign substances, and this leads to the above-described defects. Since quality requirements for color filters are becoming increasingly severe, it is desired to eliminate these defects and to produce high quality color filters.
Another problem is a limit in contents of the liquid crystal compound in the solution, because the polymerizing liquid crystal compound does not easily dissolve in organic solvents. Therefore, a viscosity of the solution is low, and this solution cannot form an even and thick layer.
In order to solve this problem, it is considerable to add a small amount of polymer into the solution. However, the added polymer interferes the orientation of the liquid crystal, and therefore it is impossible to produce a high performance color filter in this approach.
Japanese Patent Application Laid-Open (JP-A) No. 2000-154168 discloses a cross-linking liquid crystal composition which comprises a particular macromolecular acrylic photoisomerizing chiral compound and a liquid crystal polymer, which composition can be coated in a solution state. A viscosity of this composition can be adjusted by changing a ratio of a solvent, however, the composition has a drawback that reorientation of the liquid crystal takes long time.
When a layer containing the liquid crystal composition (color filter forming layer) is formed by coating for producing a color filter, particularly in the case of a low molecular weight liquid crystal, even if the liquid crystal molecules are oriented in the horizontal direction of the substrate at the substrate side of the color filter forming layer, the liquid crystal molecules become vertical at the other side of the color filter forming layer at an air-interface side. This cause an angle of inclination (pretilt angle) of the liquid crystal molecules to continuously change in the thickness direction of the color filter forming layer. Therefore, usually, it is necessary to sandwich the layer with orientation films from both sides. However, when the liquid crystal composition is polymerized and is used as an optical film, at least one of the orientation films needs to be removed after the polymerization in order to reduce a weight and/or a thickness of the optical film. This has caused problems such as an increase in the number of required steps, for example, placement and removal of the orientation films, and an increase in wastes.
In view of the above-described problems, objects of the present invention is to provide a liquid crystal composition which can be used to produce a color filter without various defects; a color filter without various defects which is produced using the liquid crystal composition; and a liquid crystal display device employing the color filter. The present invention is further directed to provide a liquid crystal composition which controls orientation of liquid crystal molecules during production of a color filter, thereby allowing omission of one of orientation films, and suppresses contamination of dust, thereby forming an even and thick film without coating defects; a color filter having constant selective reflection wavelengths and a high reflectance, produced using the liquid crystal composition; and a liquid crystal display device employing the color filter.
The above objects are accomplished by providing the following liquid crystal composition, color filter and liquid crystal display device.
A first aspect of the liquid crystal composition of the present invention is a liquid crystal composition comprising: a liquid crystal compound, which includes at least one polymerizing group; a chiral agent; and a polymerization initiator; wherein the liquid crystal composition is filtered using a filter having a pore size of not more than 1 xcexcm.
A second aspect of the liquid crystal composition of the present invention is the liquid crystal composition of the first aspect, wherein the filtration is carried out while the liquid crystal composition is being heated.
A third aspect of the liquid crystal composition of the present invention is the liquid crystal composition of the first aspect, wherein the chiral agent is photo-reactive.
A fourth aspect of the liquid crystal composition of the present invention is the liquid crystal composition of the first aspect, wherein the liquid crystal composition has a viscosity of not more than 100 cP.
A fifth aspect of the liquid crystal composition of the present invention is the liquid crystal composition of the first aspect, further comprising a surfactant.
A sixth aspect of the liquid crystal composition of the present invention is a liquid crystal composition comprising: a liquid crystal compound, which includes at least one polymerizing group; a chiral agent; a polymerization initiator; an air-interface orientation agent; and a solvent; wherein the liquid crystal composition has a viscosity from 1 to 100 cP.
A seventh aspect of the liquid crystal composition of the present invention is the liquid crystal composition of the sixth aspect, wherein a surface tension of the liquid crystal composition is not more than 50 mN/m.
An eighth aspect of the liquid crystal composition of the present invention is the liquid crystal composition of the sixth aspect, wherein the chiral agent is photo-reactive.
A first aspect of the color filter of the present invention is a color filter produced using a liquid crystal composition comprising: a liquid crystal compound including at least one polymerizing group; a chiral agent; and a polymerization initiator; wherein the liquid crystal composition is filtered using a filter having a pore size of not more than 1 xcexcm, and a rate of pixel defects in the color filter is not more than 100/m2.
A second aspect of the color filter of the present invention is the color filter of the first aspect, wherein the pixel defects are protrusions with heights of at least 2 xcexcm.
A third aspect of the color filter of the present invention is the color filter of the first aspect, wherein the pixel defects are white dots in a colored area having sizes of at least 30 xcexcm diameter.
A fourth aspect of the color filter of the present invention is the color filter of the first aspect, wherein the pixel defects are black defects having sizes of at least 30 xcexcm diameter.
A fifth aspect of the color filter of the present invention is the color filter of the first aspect, wherein the pixel defects are foreign substances having sizes of at least 3 xcexcm diameter.
A sixth aspect of the color filter of the present invention is the color filter of the first aspect, wherein the color filter is produced by a method comprising the steps of: disposing, on a substrate, a color filter forming layer, which includes the liquid crystal composition; and irradiating ultraviolet light onto the color filter forming layer.
A seventh aspect of the color filter of the present invention is a color filter for use in a liquid crystal display device, produced by a method comprising the steps of: forming an orientation film on a substrate; disposing, on the orientation film, a color filter comprising a liquid crystal composition; and irradiating ultraviolet light onto the color filter forming layer; wherein the liquid crystal composition has a viscosity from 1 to 100 cP and comprises: a liquid crystal compound including at least one polymerizing group; a chiral agent; a polymerization initiator; an air-interface orientation agent; and a solvent.
An eighth aspect of the color filter of the present invention is the color filter of the seventh aspect, wherein the color filter forming layer is formed by being coated using at least one of bar coating, spin coating and slit coating.
A ninth aspect of the color filter of the present invention is the color filter of the seventh aspect, wherein a thickness of the color filter forming layer from 1.5 to 4 xcexcm.
A first aspect of the liquid crystal display device of the present invention is a liquid crystal display device comprising: a pair of substrates, at least one of which transmits light; and at least a color filter, a liquid crystal layer and a liquid crystal driving electrode disposed between the substrates; wherein the color filter is produced using a liquid crystal composition comprising a liquid crystal compound including at least one polymerizing group; a chiral agent; and a polymerization initiator, the liquid crystal composition being filtered using a filter having a pore size of not more than 1 xcexcm, and a rate of pixel defects in the color filter is not more than 100/m2.
A second aspect of the liquid crystal display device of the present invention is a liquid crystal display device comprising a color filter produced by a method comprising the steps of: forming an orientation film on a substrate; disposing, on the orientation film, a color filter forming layer comprising a liquid crystal composition; and irradiating ultraviolet light onto the color filter forming layer; wherein the liquid crystal composition includes at least one polymerizing group; a chiral agent; a polymerization initiator; an air-interface orientation agent; and a solvent, and the liquid crystal composition has a viscosity from 1 to 100 cP.